1. Field of the Invention
The present invention relates to a steering apparatus for a four-wheeled vehicle. This steering apparatus is used to transmit a steering force applied to a handle, which is connected to a steering shaft, through a reduction gear mechanism, a steering lever and a pair of tie rods to knuckles, which support right and left wheels, respectively.
2. Description of the Related Art
A steering apparatus for a four-wheeled vehicle, particularly, a low-speed utility vehicle is provided with a rack-and-pinion reduction gear mechanism (steering gear mechanism). The rack-and-pinion reduction gear mechanism includes a pinion connected to a steering shaft, and a rack engaged with the pinion and capable of moving to right and left, i.e., in the direction along the width of a vehicle. The opposite ends of the rack are connected to right and left knuckles by tie rods, respectively.
The long rack of the rack-and-pinion reduction gear mechanism is disposed so as to extend and move laterally, and hence the right and left tie rods are inevitably short. In case that such short tie rods are used, the position of the rack with respect to the back-and-forth direction cannot be spaced a long distance apart from the position of the joint of the knuckle and the tie rod. Therefore, the flexibility of the positioning of the rack is strictly restricted.
If the rack is disposed far ahead of the joints of the knuckles and the tie rods with respect to the back-and-forth direction to secure a wide space for driver""s feet on a step, the mounting angles of the tie rods become large. As a result, a high steering force is necessary. Thus, the position of the rack along the back-and-forth direction must be in a narrow range to achieve a low steering force by making the mounting angles of the tie rods small. On the other hand, the mounting angles of the tie rods must be large to secure a wide space for driver""s feet. As a result, a high steering force is inevitably caused.
Another type of steering apparatus includes a spur gear type reduction gear mechanism with a set of pinion and spur gear instead of rack and pinion. Long tie rods can be used because the spur gear does not need a wide lateral space. Even if the reduction gear mechanism is disposed far ahead of the joints of the knuckles and the tie rods, the mounting angles of the tie rods can be small. As a result, a low steering force can be achieved. This kind of steering apparatus with the spur gear type reduction gear mechanism is disclosed in Japanese Laid-Open Publication No. 292224/1992.
It is an object of the present invention to provide a steering apparatus with a spur gear type reduction gear mechanism which is capable of eliminating backlash in the reduction gear mechanism by simple constitutions and of giving the driver an improved steering feeling.
According to the present invention, a steering apparatus for a four-wheeled vehicle, comprises: a steering shaft adapted to be rotated by a handle; a reduction gear mechanism operatively connected to the steering shaft; the reduction gear mechanism including a pinion gear, a steering gear engaged with the pinion gear, a gear case in which the pinion gear and the steering gear are housed, and a pinion shaft on which the pinion gear is mounted, the pinion shaft being connected to the steering shaft; a steering lever operatively connected to the reduction gear mechanism; right and left tie rods operatively connected to the steering lever; and right and left knuckles operatively connected to the right and the left tie rods, respectively; a lever shaft on which the steering gear is mounted and being combined with the steering lever, a spring biasing the lever shaft so that the steering shaft is pressed against the pinion gear.
Preferably, the lever shaft has first and second end portions on first and second sides which are located on opposite sides with respect to a position at which the steering gear is connected to the lever shaft, the first end portion being supported by a bearing on the gear case and the second end portion being supported with a radial clearance by a bearing hole formed in the gear case.
Preferably, the clearance between the bearing hole and the lever shaft is formed so as to permit the lever shaft to move only in a direction in which the lever shaft is biased by the spring.
Preferably, the spring is disposed on the second side on which the bearing hole is formed.
Preferably, the spring comprises a compression coil spring and a plunger which is biased forward by the compression coil spring to press the second end portion of the lever shaft forward.
Preferably, the plunger includes a recess which is in close contact with a rear surface of the lever shaft.
Preferably, the plunger includes a V-shaped groove which is in contact with a rear surface of the lever shaft.
Preferably, the plunger includes a flat surface which is in contact with a rear surface of the lever shaft.
Preferably, the spring is disposed on the first side on which the bearing is disposed.
Preferably, the spring comprises a compression coil spring and a plunger which is biased forward by the compression coil spring to press the second end portion of the lever shaft forward.
Preferably, the plunger includes a recess which is in close contact with a rear surface of the lever shaft.
Preferably, the plunger includes a V-shaped groove which is in contact with a rear surface of the lever shaft.
Preferably, the plunger includes a flat surface which is in contact with a rear surface of the lever shaft.
Preferably, the bearing has a convex inner surface on which the lever shaft is supported so that the lever shaft is able to swing back-and-forth.
Preferably, the steering gear is a sector gear of which an axis is aligned with an axis of the lever shaft.
Preferably, the gear case is provided in its front end portion with an upper boss and a bottomed lower boss for supporting the pinion shaft, a lower end portion of the pinion shaft being fitted in a bore formed in the lower boss, and an upper end portion of the pinion shaft being supported in a ball bearing which is fitted in the upper boss.